1. Field of the Invention
The present invention relates to a method for detecting a zero track position suitable for a disk drive device for recording and/or reproducing information on and/or from an information recording medium in a disk shape, particularly to such a detecting method for a so-termed "hard disk device" in which a recording medium is stored in a closed chamber and rotated at a high speed.
2. Description of the Prior Art
Various types of disk devices have been widely utilized. In particular, a hard type magnetic disc device is normally used if a compact disk and a large data storage capacity are required. In these magnetic disk devices, a high seek speed and seek accuracy are the most significant matters because the rotation speed of the magnetic disk is very high and the data recording, or storage density is high. While seeking, the zero track position at the outermost portion of the magnetic disk is used as a reference position, so that the precise detection for the zero track position is necessarily required in the magnetic disk device.
A typical hard disk device is illustrated in FIG. 4. The hard disk device mainly includes a magnetic disk 1 for recording information; a magnetic head 2 for recording and reproducing the information on and from the disk 1; a direct drive motor (simply referred to as a "DD" motor, not shown) for rotating the magnetic disk 1; and a head drive mechanism for transporting the magnetic head 2 to a predetermined track on the magnetic disk 1. The hard disk device further includes a base plate 5 functioning as a housing base for storing the magnetic disk 1 and the magnetic head 2, and for holding them under the closed condition; a printed circuit board 6 on which a motor drive circuit, a control circuit and so on are fabricated; and a frame (not shown) for mounting the printed circuit board 6 on the base plate 5.
In the magnetic disc apparatus shown in FIG. 4, two sheets of the magnetic disc 1 are employed, and a magnetic head 2 is employed for each magnetic recording surface of a single disk 1. That is to say, four magnetic heads 2 are employed in total because both surfaces of a single disk 1 are used for recording the information thereon. These magnetic heads are mounted via a cantilever support spring on a swing arm 8 of the head drive mechanism 4. The head drive mechanism 4 is constituted by this swing arm 8, a steel belt 9 partially mounted on the swing arm 8; a pulley 10 for winding an intermediate portion of the steel belt 9 thereon; and a stepping motor 11. The pulley 10 on which the steel belt 9 is wound, is inserted into the drive shaft of the stepping motor 11 and fixed thereon. By driving the stepping motor 11, the above swing arm 8 can be swung around a rotating shaft 8a.
A housing for storing therein the magnetic disk 1, the magnetic head 2, the swing arm 8, the steel belt 9 and the pulley 10 etc. is constructed of the above-described base plate 5 and a top cover (not shown). A gasket is employed in the contact portion between the base plate 5 and the top cover, and the mount portion of the stepping motor 11 so as to maintain the closed conditions. The shaft part of the DD motor 3 is filled with a magnetic fluid. A shutter 17 is mounted on the side 8b of the swing arm 8 opposite to the head mounting side thereof. At the closed chamber side 5a of the base plate 5, a photointerruptor 18 is employed as an outside sensor. The above-described shutter 17 is positioned in such a manner that the shutter can be loosely inserted into an insertion path 18a of the photointerruptor 18. In the illustrated prior art, when the magnetic head 2 reaches the zero track position located in the outer circle of the magnetic disk 1, the photointerruptor 18 interrupts the optical path formed in the insertion path 18a of the photointerruptor 18.
During the zero track restore, the magnetic head 2 accesses at a lower speed and immediately stops at the zero track. Otherwise, if the magnetic head 2 is driven to access the zero track at a high speed, the head 2 cannot stop at the zero track.
Another conventional system in which neither optical detecting means such as the photointerruptor 18, nor mechanical detecting means is employed, is described in, for instance, European Patent Application 84308193.6 (Publication No. 0154085).
This prior art idea is characterized by setting:
a data track region essentially consisting of a plurality of information recording/reproducing tracks which are concentric circles in turn in the radial direction of the magnetic disk; PA1 a guard band region essentially consisting of tracks only for reproducing information which are positioned at the outer circumference of the data track region; and PA1 a positional information region for determining whether or not the magnetic disk opposite position of the magnetic disk is located in the data track region or the guard band region at a part of each track of both the data track region and the guard band region. In addition, the reference track detecting means control a positioning motor to transport the magnetic head each track width in accordance with the positional information of the positional information region read by the magnetic head. Thereafter, the magnetic head is transferred to the data track region, and the O-th track is detected as the reference track by detecting a change of the positional information from the positional information of the guard band region to that of the guard band region. PA1 forming an information recorded region at least on a part of said concentrically formed tracks, into which data has been previously recorded; PA1 forming an information non-recorded region on said tracks outside said information recorded region; and PA1 detecting a boundary position between said information recorded region from which said data is detectable, and said information non-recorded region from which said data is not detectable, whereby a position of the track from which said data is first of all detectable is assumed to be a zero track.
When the power supply is turned off, the actual track position of the magnetic head is unknown. Accordingly, when restoring the head to the zero track, the following cases are present. In the first case, the magnetic head is always returned to the zero track, and the track counter is aligned with the head position by resetting the track counter in the drive. When the seek error occurs, the restoring operation is required to confirm the head position. Finally, the magnetic head is merely moved to seek the zero track. Anyway, a certain detecting means is required to detect the zero position. As such a zero track detecting means, there are the first-mentioned optical detecting means, and the magnetic detecting means which is suitable for seeking such a zero track by detecing the rotation angle of the stepping motor. According to these mechanical detecting means, the sensor must be provided adjacent to the transport region and the rotation region of the swing arm 8 and the stepping motor 11. As a result, even if a compact mechanism is required, it is practically difficult to mount the sensor on the above regions, which makes it difficult to manufacture a compact and slim mechanism. When the recording density becomes, on the other hand, high, severe precision in restoring to track zero is necessarily required. Since, as is known in the art, the resolution of the optical sensor is limited, the manufacturing cost is increased if the higher resolution is required.
Moreover, in the latter prior art where there are employed the data track region and the positional information region bridged over the guard band region, and the zero track is detected based upon the positional information added to this positional information region, it is necessary to inhibit the data from being written into the positional information region. If such an inhibit writ region is present in the radial direction of the magnetic disk, the data write region as to a single track is necessarily narrowed. Accordingly, the rotation speed of the magnetic disk must be lowered. If one is lowering the rotation speed, then the error rate becomes high.
The present invention is made in consideration of the above-defined conventional drawbacks, and has therefore an object to provide a zero track detecting method, whereby the rotation speed of the information recording disk can be maintained at a relatively high value, and also no zero track detecting device such as the optical detecting device and the mechanical detecting device is required.